DNS Privacy, Authorization, Special Uses, Encoding, Characters, Matching, and Root Structure: Time for Another Look?
draft-klensin-dns-function-considerations-03

Network Working Group                                         J. Klensin
Internet-Draft                                             June 26, 2017
Intended status: Informational
Expires: December 28, 2017

    DNS Privacy, Authorization, Special Uses, Encoding, Characters,
          Matching, and Root Structure: Time for Another Look?
              draft-klensin-dns-function-considerations-03

Abstract

   The basic design of the Domain Name System was completed almost 30
   years ago.  The last half of that period has been characterized by
   significant changes in requirements and expectations, some of which
   either require changes to how the DNS is used or that can be
   accommodated only poorly or not at all.  This document asks the
   question of whether it is time to either redesign and replace the DNS
   to match contemporary requirements and expectations (rather than
   continuing to try to design and implement incremental patches that
   are not fully satisfactory) or to draw some clear lines about
   functionality that is not really needed or that should be performed
   in some other way.

Author's Note

   This draft is intended to draw a number of issues and references
   together in one place and to start a discussion.  It is obviously
   incomplete, particularly with regard to the list of perceived issues
   and deficiencies with that DNS.  To avoid misunderstanding, I don't
   completely believe some of the deficiencies listed below but am
   merely providing information about claims of deficiencies.  Input is
   welcome, especially about what is missing (or plain wrong) and would
   be greatly appreciated.

   This document should be discussed on the IETF list or by private
   conversation with the author.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 28, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Background and Hypothesis . . . . . . . . . . . . . . . . . .   4
   3.  Warts and Tensions With The Current DNS . . . . . . . . . . .   5
     3.1.  Multiple address types  . . . . . . . . . . . . . . . . .   5
     3.2.  Matching Part I: Case Sensitivity in Labels and Other
           Anomalies . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Matching Part II: Non-ASCII ("internationalized") Domain
           Name Labels . . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Matching Part III: Label Synonyms, Equivalent Names, and
           Variants  . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.5.  Query Privacy . . . . . . . . . . . . . . . . . . . . . .   9
     3.6.  Alternate Name Spaces for Public Use in the DNS
           Framework: The CLASS Problem  . . . . . . . . . . . . . .   9
     3.7.  Loose Synchronization . . . . . . . . . . . . . . . . . .   9
     3.8.  Private Name Spaces and Special Names . . . . . . . . . .  10
     3.9.  Alternate Query or Response Encodings . . . . . . . . . .  11
     3.10. Distribution and Managment of Root Servers  . . . . . . .  11
     3.11. Identifiers Versus Brands and Other Convenience Names . .  12
     3.12. A Single Hierarchy with a Centrally-controlled Root . . .  13
     3.13. Newer Application Protocols and New Requirements  . . . .  13
       3.13.1.  The Extensions . . . . . . . . . . . . . . . . . . .  13
       3.13.2.  Extensions and Deployment Pressures -- The TXT
                RRTYPE . . . . . . . . . . . . . . . . . . . . . . .  14
       3.13.3.  Periods and Zone Cut Issues  . . . . . . . . . . . .  15

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     3.14. Scaling of Reputation and Other Ancillary Information . .  16
     3.15. Tensions among transport, scaling and content . . . . . .  17
   4.  Searching and the DNS - An Historical Note  . . . . . . . . .  17
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  25
     A.1.  Changes from version -00 (2017-06-02) to -01  . . . . . .  25
     A.2.  Changes from version -01 (2017-06-06) to -02  . . . . . .  25
     A.3.  Changes from version -02 (2017-06-19) to -03  . . . . . .  25
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   This document explores contemporary expectations of the Internet's
   domain system (DNS) and compares them to the assumptions and
   properties of the DNS design.  It is primarily intended to ask the
   question of whether the differences are causing enough stresses on
   the system, stresses that cannot be resolved satisfactorily by
   further patching, that the Internet community should be considering
   designing a new system, one that is better adapted to current needs
   and expectations, and developing a deployment and transition strategy
   for it.  For those (perhaps the majority of us) for whom actually
   replacing the DNS is too radical to be realistic, the document may be
   useful in two other ways.  It may provide a foundation for discussing
   what functions the DNS should not be expected to support and how
   those functions can be supported in other ways, perhaps via an
   intermediate system that then calls on the DNS or by using some other
   type of database technology for some set of functions while leaving
   the basic DNS functions intact.  Or it may provide a basis for
   "better just get used to that and the way it works" discussions to
   replace fantasies about what the DNS might do in some alternate
   reality.

   There is a key design or philosophical question associated with the
   analysis in this document that the document does not address.  It is
   whether changes to perceived requirements to DNS functionality as
   described here are, in most respects, evolutionary or whether many of
   them are instances of trying to utilize the DNS for new requirements
   because it exists and is already deployed independent of whether the
   DNS is really appropriate or not.  The latter might be an instance of
   a problem often described in the IETF as "when all you have is a
   hammer, everything looks like a nail".

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   While this document does not assume deep technical or operational
   knowledge of the DNS, it does assume some knowledge and at least
   general familiarity with the concepts of RFC 1034 [RFC1034] and RFC
   1035 [RFC1035] and the terminology discussed in RFC 7719 [RFC7719]
   and elsewhere.  Although some of the comments it contains might be
   taken as hints or examples of different ways to think about the
   design issues, it makes no attempt to explore, much less offer a
   tutorial on, alternate naming systems or database technologies.

   It is perhaps worth noting that, while the perspective is different
   and more than a dozen years have passed, many of the issues discussed
   in this document were analyzed and described (most of them with more
   extensive explanations) in a 2005 US National Research Council report
   [NRC-Signposts].

   Readers should note that several references are to obsolete
   documents.  That was done because they are intended to show the
   documents and dates that introduced particular features or concepts.
   When current versions are intended, they are referenced.

2.  Background and Hypothesis

   The domain name system (DNS) [RFC1034] was designed starting in the
   early 1980s [RFC0799] [RFC0881] [RFC0882] with the main goal of
   replacing the flat, centrally-administered, host table system
   [RFC0810] [RFC0952] [RFC0953] with a hierarchical, administratively-
   distributed, system.  The DNS design included some features that,
   after initial implementation and deployment, were judged to be
   unworkable and either replaced (e.g., the mail destination (MD) and
   mail forwarder (MF) approach [RFC0882] that were replaced by the MX
   approach [RFC0974]), abandoned (e.g., the mechanism for using email
   local parts as labels described in RFC 1034 Section 3.3), or
   deprecated (e.g., the WKS RR TYPE [RFC1123].  Newer ideas and
   requirements have identified a number of other features, some of
   which were less developed than others.  Of course the original
   designers could not anticipate everything that has come to be
   expected of the DNS in the last 30 years.

   In recent years, demand for new and extended services and uses of the
   DNS have, in turn, led to proposals for DNS extensions or changes of
   various sorts.  Some have been adopted, including a model for
   negotiating extended functionality [RFC2671], others were found to be
   impracticable, and still others continue to be under consideration.
   A few features of the original DNS specification, such as the CLASS
   property and label types, have also been suggested to be so badly
   specified that they should be deprecated [Sullivan-Class].

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   Unlike earlier changes such as the IDNA mechanisms for better
   incorporating non-ASCII labels without modifying the DNS structure
   itself [RFC3490] [RFC5890], some recent proposals require or strongly
   suggest changes to APIs, formats, or interfaces by programs that need
   to retrieve information from the DNS or interpret that information.
   Differences between the DNS architecture and the requirements that
   imply them suggest that it may be time to stop patching the DNS or
   trying to extend it in small increments, but to consider moving some
   functionality elsewhere or development of a new system that better
   meets today's needs and a transition strategy to it.

   The next section of this document discusses a number of issues with
   the current DNS design that could appropriately be addressed by a
   different and newer design model.  In at least some cases, changing
   the model and protocols could bring significant benefits to the
   Internet and/or its administration.

   This document is not a proposal for a new protocol.  It is intended
   to stimulate thought about how far we want to try to push the
   existing DNS, to examine whether expectations of it are already
   exceeding its plausible capabilities, and to start discussion of a
   redesign or alternatives to one if the time for that decision has
   come.

3.  Warts and Tensions With The Current DNS

   As suggested above, there are many signs that the DNS is incapable of
   meeting contemporary expectations of how it should work and
   functionality it should support.  Some of those expectations are
   unrealistic under any imaginable circumstances; others are impossible
   (or merely problematic) in the current DNS structure but could be
   accommodated in a redesign.  These are examples, rather than a
   comprehensive list, and do not appear in any particular order.

3.1.  Multiple address types

   While returning both TYPE A (IPv4 address) and AAAA (IPv6 address)
   records as additional information in response to any of several query
   types (see RFC 3596 [RFC3596]) was a useful patch, it is easy to
   imagine better choices.  For example, except that it would have
   required DNS modifications, we could have established a single
   "address" query type (QTYPE) that could return whatever IPv4 and/or
   IPv6 addresses were available, perhaps with preference information if
   that were stored in the database, and without requiring the "ANY" be
   used.  Other solutions would have been plausible; that one is offered
   only to combine an existence proof of at least one possibility and an
   example of how the existing DNS design and implementations are
   preventing us from thinking more broadly about possible solutions.

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3.2.  Matching Part I: Case Sensitivity in Labels and Other Anomalies

   The DNS specifications assume that labels are octet strings and
   octets with the high bit zero have seven-bit ASCII codes in the
   remaining bits.  They require that, when a domain name used in a
   query is matched to one stored in the database, those ASCII
   characters be interpreted in a case-independent way, i.e., upper and
   lower case letters are treated as equivalent (digits and symbols are
   not affected) [RFC4343].  For non-ASCII octets, i.e., octets in
   labels with the first bit turned on, there are no assumptions about
   the character coding used, much less any rules about character case
   equivalence -- strings must be compared by matching bits in sequence.
   Even though the current model for handling non-ASCII (i.e.,
   "internationalized") domain name labels (IDNs) [RFC5890] (and see
   Section 3.3 below) encodes information so the DNS is not directly
   affected, the notion that some characters in labels are handled in a
   case-insensitive way and that others are case-sensitive (or that
   upper case must be prohibited entirely as IDNA does) has caused a
   good deal of confusion and resentment.  Those concerns and complaints
   about inconsistent behavior and mishandling (or suboptimal handling)
   of case relationships for some languages have not been mitigated by
   repeated explanations that the relationships between "decorated"
   lower-case characters and their upper-case equivalents are often
   sensitive to language and locality and therefore not deterministic
   with information available to DNS servers.

3.3.  Matching Part II: Non-ASCII ("internationalized") Domain Name
      Labels

   Quite independent of the case-sensitivity problem, one of the
   fundamental properties of Unicode [Unicode] is that some abstract
   characters can be represented in multiple ways, such as by a single,
   precomposed, code point or by a base code point followed by one or
   more code points that specify combining characters.  While Unicode
   Normalization can be used to eliminate many (but not all) of those
   distinctions for comparison (matching) purposes, it is best applied
   during matching rather than by changing one string into another.  The
   first version of IDNA ("IDNA2003") made the choice to change strings
   during processing for either storage or retrieval [RFC3490]
   [RFC3491]; the second ("IDNA2008") required that all strings be
   normalized and that upper case characters are not allowed at all
   [RFC5891].  Neither is optimal, if only because, independent of where
   they are changed if they are changed at all, transforming the strings
   themselves implies that the input string in an application may not be
   the same as the string used in processing and perhaps later display.

   It would almost certainly be preferable, and more consistent with
   Unicode recommendations, to use normalization (and perhaps other

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   techniques if they are appropriate) at matching time rather than
   altering the strings at all, even if there were still only a single
   matching algorithm, i.e., normalization were added to the existing
   ASCII-only case folding.  However, even Unicode's discussion of
   normalization [Unicode-UAX15] indicates that there are special,
   language-dependent, cases (the most commonly-cited example is the
   dotless "i" (U+0131)).  Not only does the DNS lack any information
   about languages that could be used in a mapping algorithm, but, as
   long as there is a requirement that there be only one mapping
   algorithm for the entire system, that information could not be used
   even if it were available.  One could imagine a successor system that
   would use information stored at nodes in the hierarchy to specify
   different matching rules for subsidiary nodes (or equivalent
   arrangements for non-hierarchical systems).  It is not clear whether
   that would be a good idea, but it certainly is not possible with the
   DNS as we know it.

3.4.  Matching Part III: Label Synonyms, Equivalent Names, and Variants

   As the initial phases of work on IDNs started to conclude, it became
   obvious that the nature and evolution of human language and writing
   systems required treating some names as "the same as" others.  The
   first important example of this involved the relatively recent effort
   to simplify the Chinese writing system, thereby creating a
   distinction between "Simplified" and "Traditional" Chinese even
   though the meaning of the characters remained the same in almost all
   cases (in so-called ideographic character sets, characters have
   meaning rather than representing sounds).  A joint effort among the
   relevant country code top level domain (TLD) registries and some
   other interested parties produced a set of recommendations for
   dealing with the issues with that script [RFC3743] and introduced the
   concept of "variant" characters and domain names.

   However, when names are seen as having meanings, rather than merely
   being mnemonics, especially when they represent brands or the
   equivalent, or when spelling for a particular written language is not
   completely standardized, demands to treat different strings as exact
   equivalents are obvious and inevitable.  As a trivial English-
   language example, it is widely understood that "colour" and "color"
   represent the same word, so does that imply that, if they are used as
   DNS labels in domain names all of whose other labels are identical,
   the two domain names should be treated as identical?  Examples for
   other languages or writing systems, especially ones in which some or
   all markings that distinguish characters or words by sound or tone or
   that change the pronunciation of words are optional, are often more
   numerous and more problematic than national spelling differences in
   English, but they are harder to explain to those unfamiliar with
   those other languages or writing systems (and hard to illustrate in

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   ASCII-only Internet-Drafts and RFCs).  Although approximations are
   possible, the DNS cannot handle that requirement: not only do its
   aliasing mechanisms (CNAME, DNAME, and various proposals for newer
   and different types of aliasing [DNS-Aliases] [DNS-BNAME], not
   provide a strong enough binding, but the ability to use those aliases
   from a subtree controlled by one administrative entity to that of
   another one implies that there is little or no possibility of the
   owner (in either the DNS sense or the registrar-registrant one) of a
   particular name to control the synonyms for it.  Some of that issue
   can be dealt with at the application level, e.g., by redirects in web
   protocols, but taking that approach, which is the essential
   characteristic of "if both names belong to the same owner, everything
   is ok" approaches, results in names being handled in inconsistent
   ways in different protocols.

   A different way of looking at part of this issue (and, to some
   degree, of the one discussed above in Section 3.3) is that these
   perceived equivalences and desired transformations are context-
   dependent, but the DNS resolution process is not [RFC6912].

   Similar problems arise as people notice that some characters are
   easily mistaken for others and that might be an opportunity for user
   confusion and attacks.  Commonly-cited examples include the Latin and
   Cyrillic script "a" characters, which are identical [CACM-Homograph],
   the characters in many scripts that look like open circles or
   vertical or horizontal lines, and even the Latin script letter "l"
   and the European digit "1", but examples abound in other scripts and
   combinations of scripts as well.  The most common proposed solution
   within the DNS context has been to treat these cases, as well as
   those involving orthographic variations, as "variants" (but variants
   different from the system for Chinese characters mentioned above) and
   either ban all but one (or a few) of the possible labels from the DNS
   (possibly on a first come first served basis) or by ensuring that any
   collection of such strings that are delegated as assigned to the same
   ownership (see above).  Neither solution is completely satisfactory:
   if all but one string is excluded, users who guess at a different
   form, perhaps in trying to transcribe characters from written or
   printed form, don't find what they are looking for and, as pointed
   out above, "same ownership" is sufficient only with carefully-
   designed and administered applications protocol support and sometimes
   not then.

   Some of these issues are discussed at more length in an ICANN report
   [ICANN-VIP].

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3.5.  Query Privacy

   There has been growing concern in recent years that DNS queries occur
   in clear text on the public Internet and that, if those queries can
   be intercepted, they can expose a good deal of information about
   interests and contacts that could compromise individual privacy.
   While a number of proposals, including query name minimization
   [RFC7816] and running DNS over an encrypted tunnel [RFC7858], have
   been made to mitigate that problem, they all appear to share the
   common properties of security patches rather than designed-in
   security or privacy mechanisms.  While experience may prove otherwise
   once (and if) they are widely deployed, it does not appear that any
   of them are as satisfactory as a system with query privacy designed
   in might be.  More general tutorials on this issue have appeared
   recently [Huston-DNSPrivacy].

3.6.  Alternate Name Spaces for Public Use in the DNS Framework: The
      CLASS Problem

   The DNS standards include specification of a CLASS value to "identify
   a protocol family or instance of a protocol" [RFC 1034, Section 3.6
   and elsewhere].  While CLASS was used effectively in the early days
   of the DNS to manage different protocol families within the same
   administrative environment, recent attempts to use it to either
   partition the DNS namespace in other ways such as for non-ASCII names
   (partially to address the issues in Section 3.2 Section 3.3) or to
   use DNS mechanisms for entirely different namespaces have exposed
   fundamental problems with the mechanism [Sullivan-Class], leading to
   recommendations that it be dropped entirely.

   Whether either the function CLASS was originally intended to provide
   or the ones for which there have been attempts to use it more
   recently are actually needed is a separate question; it is clear that
   the current DNS technical and administrative model is unsuitable for
   either function.

3.7.  Loose Synchronization

   The DNS model of master and slave servers, with the latter initiating
   updates based on expiration interval values, and local caches with
   updates based on TTL values, depends heavily on an approach that has
   come to be called "loose synchronization", i.e., that there can be no
   expectation that all of the servers that might reasonably answer a
   query will have exactly the same data unless those data have been
   unchanged for a rather long period.  Put differently, if some or all
   of the records associated with a particular node in the DNS
   (informally, a fully-qualified domain name (FQDN)) change, one cannot
   expect those changes to be propagated immediately.

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   That model has worked rather well since the DNS was first deployed,
   protecting the system from requirements for mechanisms that are
   typical where simultaneous update of multiple systems is needed.
   Such mechanisms include elaborate locking, complex update procedures
   and handshaking, or journaling.  As has often been pointed out with
   the Internet, implementation and operational complexity are often the
   enemy of stability, security, and robustness.  Loose synchronization
   has helped keep the DNS as simple and robust as possible.

   A number of recent ideas about using the DNS to store data for which
   important changes occur very rapidly are, however, largely
   incompatible with loose synchronization.  Efforts to use very short
   (or zero) refresh times (in SOA records for slave updates from
   masters) and TTLs (for caches) to simulate nearly-simultaneous
   updating may work up to a point but appear to impose very heavy loads
   on servers and distribution mechanisms that were not designed to
   accommodate that style of working.  Similar observations can be made
   about attempts to use the NOTIFY extension [RFC1996] or dynamic,
   "server-push", updating rather than the traditional DNS mechanisms.
   While the NOTIFY and push mechanisms normally provide refresh times
   and update mechanisms faster than those specified in RFC 1034 and
   1035, they imply that a "master" server must know the identities of
   (and have good connectivity to all of) its slaves.  That defeats at
   least some of the advantages associated with stealth slaves,
   particularly those associated with reduction of query traffic across
   the Internet.  Those mechanisms do nothing for cache updates: unless
   servers keep track of the source of every query for names associated
   with a specific zone and then somehow notify the query source
   systems, the only alternative to having information that might be
   obsolete stored in caches is to use very short or zero TTLs so the
   cached data time out almost immediately after being stored (or are
   not stored at all), requiring a new query to an authoritative server
   each time a resolver attempts to look up a name.

3.8.  Private Name Spaces and Special Names

   Almost since the DNS was first deployed, there have been situations
   in which it is desirable to use DNS-like names, and often DNS
   resolution mechanisms or modifications of them, with name spaces for
   which globally-available and consistent resolution using the public
   DNS is either unfeasible or undesirable (and for which the use of
   CLASS is not an appropriate mechanism).  The need to isolate names
   and addresses on LANs from the public Internet, typically via "split
   horizon" approaches, is one example of this requirement although
   often not recognized as such.  Another example that has generated a
   good deal of controversy involves "special names" -- labels or
   pseudo-labels, often in TLD positions, that signal that the full name

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   should not be subject to normal DNS resolution or other processing
   [RFC6761] [DNSOP-Sutld].

   Independent of troublesome policy questions about who should allocate
   such names and the procedures to be used, they almost inherently
   require either a syntax convention to identify them (there actually
   was such a convention, but it was abandoned many years ago and there
   is no plausible way to re-institute it) or tables of such names that
   are known to, and kept updated on, every resolver on the Internet, at
   least if spurious queries to the root servers are to be avoided.

   If the DNS were to be redesigned and replaced, we could recognize
   this requirement as part of the design and handle it much better than
   it is possible to handle it today.

3.9.  Alternate Query or Response Encodings

   The DNS specifies formats for queries and data responses, based on
   the state of the art and best practices at the time it was designed.
   Recent work has suggested that there would be significant advantages
   to supporting at least a description of the DNS messages in one or
   more alternate formats, such as JSON [Hoffman-DNS-JSON]
   [Hoffman-SimpleDNS-JSON].  While that work has been carefully done to
   avoid requiring changes to the DNS, much of the argument for having
   such a JSON-based description format could easily be turned into an
   argument that, if the DNS were being revised, that format might be
   preferable as a more direct alternative to having DNS queries and
   responses in the original form.

3.10.  Distribution and Managment of Root Servers

   The DNS model requires a collection of root servers that hold, at
   minimum, information about top-level domains.  Over the years, that
   requirement has evolved from a technically fairly minor function,
   normally carried out as a service to the broader Internet community
   and its users and systems, to a subject that is intensely
   controversial with regard to control of those servers, including how
   they should be distributed and where they should be located.  While a
   number of mechanisms have been proposed and one (anycast [RFC7094])
   is in very active use to mitigate some of the real and perceived
   problems, it seems obvious that a DNS successor, designed for today's
   global Internet and perceived requirements, could handle these
   problems in a technically more appropriate and less controversial
   way.

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3.11.  Identifiers Versus Brands and Other Convenience Names

   A key design element of the original network object naming systems
   for the ARPANET, largely inherited by the DNS, was that the names,
   while expected to be mnemonic, were identifiers and their being
   highly distinguishable and not prone to ambiguity was important.
   That led to restrictive rules about what could appear in a name.
   Those restrictions originated with the host table and even earlier
   [RFC0236] [RFC0247] and came to the DNS (largely via SMTP) as the
   "preferred syntax" [RFC 1034 Section 3.5] or what we now often call
   the letter-digit-hyphen (LDH) rule.  Similar rules to make
   identifiers easier to use, less prone to ambiguity, or less likely to
   interfere with syntax occur frequently in more formal languages.  For
   example, almost every programming language has restrictions on what
   can appear in an identifier and Unicode provides general
   recommendations about identifier composition [Unicode-USA31].  Both
   are quite restrictive as compared to the number of characters and
   total number of strings that can be written using that character
   coding system.

   In the last decade or two, another perspective has emerged, largely
   without being explicitly understood or acknowledged.  In it, the DNS
   is really (and primarily) a system for expressing thoughts and
   concepts.  Those include free expression of ideas in as close to
   natural language as possible as well as representation of product
   names and brands.  That view requires letter-like characters that
   might not be reasonable in identifiers along with a variety of
   symbols and punctuation.  It may also require indicators of preferred
   type styles to provide information in a form that exactly matches
   personal or legal preferences.  At least it carried to an extreme,
   that perspective would argue for standardizing word and sentence
   separators, for removing the 63 octet per label limit and probably
   the limit of 255 octets on the total length of a domain name, and
   perhaps even eliminating the hierarchy or allowing separators for
   labels in presentation form (now fixed at "." for the DNS) to be
   different according to context.  It suggests that, at least, the
   original design was defective in not prioritizing those uses over the
   more restrictive approach associated with prioritizing unique and
   unambiguous identifiers.

   So we have two, or, depending on how one counts, three very different
   use cases.  The historical one is support for unique identifiers.
   The other is expression of ideas and, if one considers them separate,
   presentation of brand and product names.  Because they inherently
   involve different constraints, priorities, and success criteria,
   these perspectives are, at best, only loosely compatible.

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   We cannot simultaneously optimize both the identifier perspective and
   either or both of the others in the same system.  At best, there are
   some complex trade-offs involved.  Even then, it is not clear that
   the same DNS (or other system) can accommodate all of them.  Until we
   come to terms with that, the differences manifest themselves with
   friction among communities, most often with tension between "we want
   to do (or use or sell) these types of labels" and "not good for the
   operational Internet or the DNS".

3.12.  A Single Hierarchy with a Centrally-controlled Root

   A good many Internet policy discussions in the last two decades have
   revolved around such questions of how many top level domains there
   should be, what they should be, who should control them and how, how
   (or if) their individual operations and policy decisions should be
   accountable to others, and what processes should be used (and by what
   entities or organizational structures) to make those decisions.
   Several people have pointed out that, if we were designing a next-
   generation DNS using today's technology, it should be possible to
   remove the technical requirement for a central authority over the
   root (some people have suggested that blockchain approaches would be
   helpful for this purpose; others believe they just would not scale
   adequately, at least at acceptable cost, but that other options are
   possible).  Whether elimination of a single, centrally-controlled,
   root would be desirable or not is fairly obviously a question of
   perspective and priorities.

3.13.  Newer Application Protocols and New Requirements

   New work done in other areas has led to demands for new DNS features,
   many of them involving data values that require recursively
   referencing the DNS.  Early record types that did that were
   accompanied by restrictions that reduced the risk of looping
   references or other difficulties.  For example, while the MX RRTYPE
   has a fully-qualified domain name as its data, SMTP imposes "primary
   name" restrictions that prevent the name used from being, e.g., a
   CNAME.  While loops with CNAMEs are possible, RFC 1034, Section 3.6,
   includes a discussion about ways to avoid problems and how they
   should be handled.  Some newer protocols and conventions can cause
   more stress.  There are separate issues with additions and with how
   the DNS has been extended to try to deal with them.

3.13.1.  The Extensions

   Some examples of DNS extensions for new protocol demands that
   illustrate, or have led to, increased stress include:

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   NAPTR  Requires far more complex data in the DNS for ENUM (e.g.,
      VoIP, specifically SIP) support, including URI information and
      hence recursive or repeated lookups, than any of the RRTYPEs
      originally supported.  The RRSET associate with these records can
      become quite large because the separator between the various
      records is part of the RDATA, and not the {owner, class, type}
      triple (a problem slightly related to the problem with overloading
      of TXT RTYPE discussed in Section 3.13.2).  This problem, and
      similar ones for some of the cases below. may suggest that any
      future design is in need of a different TYPE model such as
      systematic arrangements for subtypes or some explicit hierarchy in
      the TYPEs.

   URI  Has a URI as its data, typically also requiring recursive or
      repeated lookups.

   Service location (SRV) and credential information (including SPF and
   DKIM)
      Require structured data and, especially for the latter two,
      significantly more data, than most original RRTYPEs.

   URI/URL  The early design decision for the World Wide Web that its
      mechanism for identifying digital web content (now known as
      Uniform Resource Identifiers [RFC3986]) did so by using domain
      names and hence the network location of the information or other
      material.  That, in turn, has required systems intended to improve
      web performance by locating and retrieving a "nearest copy"
      (rather than the single copy designated by the URL) to intercept
      DNS queries and respond with values that are not precisely those
      stored for the designated domain name in the DNS or to otherwise
      access information in a way not supported by the DNS itself.

   In addition to the stresses these new functions cause, incremental
   deployment of systems that utilize them means that some functions
   will work in some environments and not others.  This has been
   especially problematic with complex, multi-record, functions like
   DNSSEC that provide or require special validation mechanisms.

3.13.2.  Extensions and Deployment Pressures -- The TXT RRTYPE

   Unfortunately (but unsurprisingly) and despite IETF efforts to make
   things easier [RFC6895], DNS support libraries have often been slow
   to add full support for new RRTYPEs, impeding deployment of
   applications that depend on them.  Both to get faster deployment and,
   at least until recently, to avoid burdensome IETF approval
   procedures, many application designers have chosen to push protocol-
   critical information into records with TXT RRTYPE, a record type that

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   was originally intended to include only information equivalent to
   comments.

   This causes two problems.  First, TXT records used this way tend to
   get long and complex, which is a problem in itself if one is trying
   to minimize TCP connections.  Second, applications that are
   attempting to obtain data cannot merely ask for the relevant QTYPE,
   they must obtain all of the records with QTYPE TXT and parse them to
   determine which ones are of interest.  That would be easier if there
   was some standard for how to do that parsing but, at least in part
   because the clear preference in the DNS design is for distinct
   RRTYPEs for different kinds of information, there is no such standard
   (there was a proposal in 1993 to structure the TXT DATA in a way that
   would have addressed the issue [RFC1464] but it apparently never went
   anywhere).

   On the other hand, this issue is somewhat different from most of the
   others described in this document because (as the IETF has
   recommended several times) the problem is easily solved within the
   current DNS design by allocating and supporting new RRTYPEs when
   needed rather than using TXT as a workaround (that does not mean that
   other solutions are impossible, either with the current DNS or some
   other design).  The problem then lies in the implementations and/or
   mechanisms that deter or impede rapid deployment of support for new
   RRTYPEs.

3.13.3.  Periods and Zone Cut Issues

   One of the DNS characteristics that is poorly understood by non-
   experts is that the period (".", U+002E) character can be used in
   three different ways:

   o  As a label separator in the presentation form that also designates
      a "zone break" (delegation boundary).  For example,
      foo.bar.example.com indicates the owner, "foo", of records in the
      "bar.example.com" zone.

   o  As a label separator in the presentation form that does not
      designate a zone break.  For example, foo.bar.example.com
      indicates the owner, "foo.bar", of records in the "example.com"
      zone.

   o  As a character within a label, including as a substitute for an
      at-sign ("@") when an email address appears in an SOA record or in
      a label that denotes such an address (see Section 2 above).

   In general, these cases cannot be distinguished by looking at them.
   The third is problematic for non-DNS reasons, e.g.,

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   "john.doe.example.net" is ambiguous as to whether it should be
   interpreted as a simple FQDN, as a notation for john.doe@example.net,
   for john@doe.example.net, and so on.

   The distinction between the first two cases was probably not
   important as the DNS was originally intended to be used.  However, as
   soon as RRTYPEs (other than NS records that define the zone cut) are
   used that are sensitive to the boundaries between zones, the
   distinctions become important to people other than the relevant zone
   administrators.  DNSSEC involves one such set of relationships.  It
   increases the importance of questions about what should go in a
   parent zone and what should go in child zones and how much difference
   it makes if NS records in a parent zone for a child zone are
   consistent with the records and data in the child zone.  This also
   causes application issues and may raise questions about relationships
   between registrars and one or more registries or, if they are
   separate, DNS operators.

3.14.  Scaling of Reputation and Other Ancillary Information

   The original design for DNS administration, reflected in RFC 1591
   [RFC1591] and elsewhere, assumed that all domains would exhibit a
   very high level of responsibility toward and for the community and
   that level of responsibility would be enforced if necessary.  More
   recent decisions have taken things in the direction of "registrant
   beware" and even "user and applications beware".  While some recent
   protocols and proposals at least partially reflect that original
   model of a high level of responsibility (see, e.g., IDNA [RFC5890]
   and the discussion in a recent Internet-Draft [Klensin-5891bis]),
   other decisions and actions tend to shift responsibility to the
   registrant or try to avoid accountability entirely.  One possible
   approach to the problems, especially security problems, that are
   enabled by those new trends and the associated environment is to
   establish reputation systems associated with clearly-defined
   administrative boundaries and with warnings to users, even if those
   reputation systems are managed by parties not directly associated
   with the DNS.

   The IETF DBOUND WG [IETF-DBOUND] addressed ways to establish and
   document boundaries more precise than simple dependencies on TLDs but
   it was not successful in producing a standard.

   A TLD reputation-based approach was adopted by some web browsers
   after IDNs and a growing number of gTLDs were introduced; that
   approach was based on a simple list and does not scale to the current
   size of the DNS or even the DNS root.

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3.15.  Tensions among transport, scaling and content

   The original design for the DNS envisaged a simple query and response
   protocol where both the command and the response could be readily
   mapped into a single IP packet.  The Hosts Requirement specification
   [RFC1123] required all DNS applications to accept a UDP query or
   response over UDP with up to 512 octets of DNS payload.  TCP was seen
   as a fallback when the response was greater than this 512 octet
   limit, and this fallback to use TCP as the transport protocol was
   considered to be the exception rather than the rule.

   Over the intervening years we have seen the rise of a common
   assumption of an Internet-wide Maximum Transmission Unit size of
   1,500 octets, accompanied with an assumption that UDP fragmentation
   is generally viable.  This underpins the adoption of the Extended DNS
   Options [RFC6891] to specify a UDP buffer size larger than 512 octets
   and a suggestion within that specification to use 4,096 as a suitable
   compromise as a UDP payload size.  This has proved to be fortuitous
   for the DNSSEC security extensions where the addition of DNSSEC
   security credentials in DNS responses [RFC4034] can lead to the use
   of large DNS responses.  However, this exposes some tensions over the
   handling of fragmentation in IP, where UDP fragments have been
   observed to be filtered by various firewalls.  Additionally for IPv6,
   there are the factors of filtering of the ICMPv6 Packet Too Big
   diagnostic messages, and discarding of IPv6 packets that contain
   extension headers [RFC7872].  More generally, fragmented UDP packets
   appear to have a lower level of reliability than unfragmented TCP
   packets.

   Behind this observation about relative reliability of delivery is the
   tension between the lightweight load of UDP and the downside of
   elevated probability of discarding of packet fragments as compared to
   TCP, which offers increased levels of assurance of content delivery,
   but with the associated imposition of TCP session state and the
   downside of reduced DNS scalability and increased operational cost.

4.  Searching and the DNS - An Historical Note

   Some of the issues identified above might reasonably be addressed,
   not by changing the DNS itself but by changing our model of what it
   is about and how it is used.  Specifically, one key assumption when
   the DNS (and the host table system before it) was designed was that
   it was a naming system for network resources, not, e.g., digital
   content.  As such, exact matching was important, it was reasonable to
   have labels treated as mnemonics that did not necessarily have
   linguistic or semantic meaning except to those using them, and so on.
   A return to that model, presumably by having user-facing applications
   call on an intermediate layer to disambiguate user-friendly names and

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   map them to DNS names (or network object locators more generally)
   would significantly reduce stress on the DNS and would also allow
   dealing with types of matching and similar or synonymous strings that
   cannot be handled algorithmically no matter how much DNS matching
   rules were altered.

   In some respects, search engines based on free-text analysis and
   linkages among information have come to serve many of the functions
   of such an intermediate layer.  Many studies and sources have pointed
   out that few users actually understand, much less care about, the
   distinction between a DNS name and a search term.  Recent versions of
   some web browsers have both recognized the failure of that
   distinction and reinforced it by eliminating the separation between
   "URL" and "search bar".

   It is worth noting that, while that "search" approach, or some other
   approach that abstracted and separated several of the issues
   identified in Section 3 from the DNS protocol and database
   themselves, it does not address all of them.  At least some elements
   of several of those issues, such as the synchronization ones
   described in Section 3.7 and the transport ones described in
   Section 3.15, are inherent in the DNS design and, if we are not going
   to replace the DNS, we had best get used to them.

   In the early part of the last decade, the IETF engaged in some
   preliminary exploration of the intermediate layer approach in the
   context of IDNs and what were then called "Internet keywords"
   [DNS-search].  It may be time to examine that approach again and to
   do so more deeply in the context of developments since the time of
   that earlier work and the degree to which use of an intermediate
   layer by appropriate user-facing applications might be used to
   address some of the issues identified above.

5.  Acknowledgements

   Many of the concerns and ideas described in this document reflect
   conversations over a period of many years, some rooted in DNS
   "keyword" and "search" discussions that paralleled the development of
   Internationalized Domain Names (IDNs).  Conversations with, or
   writings of, Rob Austein, Christine Borgman, Carolina Carvalho, Vint
   Cerf, Lyman Chapin, Patrik Faltstrom, Geoff Huston, Gervase Markham,
   Xiaodong Lee, Karen Liu, Yaqub Mueller, Andrew Sullivan, Paul Twomey,
   Suzanne Woolf, Jiankang Yao, other participants in the circa 2003
   "DNS Search" effort and in the ICANN SSAC Working Party on IDNs, and
   some others whose names were sadly forgotten were particularly
   important to either the content of this document or the motivation
   for writing it even though they may not agree with the conclusions I
   have reached and bear no responsibility for them.

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   Many of the subsections of Section 3 were extracted from comments
   first made in conjunctions with recent email discussions.  Comments
   from Suzanne Woolf about an early draft were particularly important
   as was material developed with suggestions from Patrik Faltstrom,
   especially Section 3.13.  Feedback and suggestions from several of
   the above and from Stephane Bortzmeyer, Tony Finch, and George
   Sadowsky were extremely helpful for improving the clarity and
   accuracy of parts of the document, especially so for a broader
   audience.  Geoff Huston made several useful comments and contributed
   most of Section 3.15.

6.  IANA Considerations

   [[CREF1: RFC Editor: Please remove this section before publication.]]

   This memo includes no requests to or actions for IANA.

7.  Security Considerations

   From both security and privacy perspectives, a replacement for the
   DNS would not have to go very far to be a significant improvement.
   Even moving some functions out of the DNS that are now a poor fit
   would provide significant opportunities for security and privacy
   improvements.

8.  References

8.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <http://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <http://www.rfc-editor.org/info/rfc1035>.

8.2.  Informative References

   [CACM-Homograph]
              Gabrilovich, E. and A. Gontmakher, "The Homograph Attack",
              Communications of the ACM 45(2):128, February 2002,
              <http://www.cs.technion.ac.il/~gabr/papers/
              homograph_full.pdf>.

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   [DNS-Aliases]
              Woolf, S., Lee, X., and J. Yao, "Problem Statement: DNS
              Resolution of Aliased Names", March 2011,
              <https://datatracker.ietf.org/doc/draft-ietf-dnsext-
              aliasing-requirements/>.

   [DNS-BNAME]
              Yao, J., Lee, X., and P. Vixie, "Bundled DNS Name
              Redirection", May 2016, <https://datatracker.ietf.org/doc/
              draft-yao-dnsext-bname/>.

   [DNS-search]
              IETF, "Internet Resource Name Search Service", 2003,
              <https://datatracker.ietf.org/wg/irnss/about/>.

              While it met several times informally and as one or more
              BOFs, this effort never really got off the ground.  That
              was due in part to the IETF decision to go forward with
              the IDNA approach and in part by signs that the "keyword"
              efforts were beginning to fall apart.

   [DNSOP-Sutld]
              Lemon, T., Droms, R., and W. Kumari, "Special-Use Domain
              Names Problem Statement", June 2017,
              <https://datatracker.ietf.org/doc/draft-ietf-dnsop-sutld-
              ps>.

   [Hoffman-DNS-JSON]
              Hoffman, P., "Representing DNS Messages in JSON", May
              2017, <https://datatracker.ietf.org/doc/draft-hoffman-dns-
              in-json/>.

   [Hoffman-SimpleDNS-JSON]
              Hoffman, P., "Simple DNS Queries and Responses in JSON",
              June 2017, <https://datatracker.ietf.org/doc/draft-
              hoffman-simplednsjsonn/>.

   [Huston-DNSPrivacy]
              Huston, G. and J. Silva Dama, "DNS Privacy", Internet
              Protocol Journal Vol 20, No 1, March 2017,
              <http://ipj.dreamhosters.com/wp-
              content/uploads/issues/2017/ipj20-1.pdf>.

   [ICANN-VIP]
              ICANN, "IDN Variant Issues Project: Final Integrated
              Issues Report Published and Proposed Project Plan for Next
              Steps is Now Open for Public Comment", February 2012,
              <https://www.icann.org/news/announcement-2012-02-20-en>.

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   [IETF-DBOUND]
              IETF, "Domain Boundaries (dbound)", 2017,
              <https://datatracker.ietf.org/wg/dbound/about/>.

   [Klensin-5891bis]
              Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Registry Restrictions and
              Recommendations", March 2017,
              <https://datatracker.ietf.org/doc/draft-klensin-idna-
              rfc5891bis/>.

   [NRC-Signposts]
              National Research Council, "Signposts in Cyberspace: The
              Domain Name System and Internet Navigation"", 2005,
              <https://www.nap.edu/catalog/11258/signposts-in-
              cyberspace-the-domain-name-system-and-internet-
              navigation>.

   [RFC0236]  Postel, J., "Standard host names", RFC 236,
              DOI 10.17487/RFC0236, September 1971,
              <http://www.rfc-editor.org/info/rfc236>.

   [RFC0247]  Karp, P., "Proffered set of standard host names", RFC 247,
              DOI 10.17487/RFC0247, October 1971,
              <http://www.rfc-editor.org/info/rfc247>.

   [RFC0799]  Mills, D., "Internet name domains", RFC 799,
              DOI 10.17487/RFC0799, September 1981,
              <http://www.rfc-editor.org/info/rfc799>.

   [RFC0810]  Feinler, E., Harrenstien, K., Su, Z., and V. White, "DoD
              Internet host table specification", RFC 810,
              DOI 10.17487/RFC0810, March 1982,
              <http://www.rfc-editor.org/info/rfc810>.

   [RFC0881]  Postel, J., "Domain names plan and schedule", RFC 881,
              DOI 10.17487/RFC0881, November 1983,
              <http://www.rfc-editor.org/info/rfc881>.

   [RFC0882]  Mockapetris, P., "Domain names: Concepts and facilities",
              RFC 882, DOI 10.17487/RFC0882, November 1983,
              <http://www.rfc-editor.org/info/rfc882>.

   [RFC0952]  Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
              host table specification", RFC 952, DOI 10.17487/RFC0952,
              October 1985, <http://www.rfc-editor.org/info/rfc952>.

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   [RFC0953]  Harrenstien, K., Stahl, M., and E. Feinler, "Hostname
              Server", RFC 953, DOI 10.17487/RFC0953, October 1985,
              <http://www.rfc-editor.org/info/rfc953>.

   [RFC0974]  Partridge, C., "Mail routing and the domain system",
              STD 10, RFC 974, DOI 10.17487/RFC0974, January 1986,
              <http://www.rfc-editor.org/info/rfc974>.

   [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts -
              Application and Support", STD 3, RFC 1123,
              DOI 10.17487/RFC1123, October 1989,
              <http://www.rfc-editor.org/info/rfc1123>.

   [RFC1464]  Rosenbaum, R., "Using the Domain Name System To Store
              Arbitrary String Attributes", RFC 1464,
              DOI 10.17487/RFC1464, May 1993,
              <http://www.rfc-editor.org/info/rfc1464>.

   [RFC1591]  Postel, J., "Domain Name System Structure and Delegation",
              RFC 1591, DOI 10.17487/RFC1591, March 1994,
              <http://www.rfc-editor.org/info/rfc1591>.

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <http://www.rfc-editor.org/info/rfc1996>.

   [RFC2671]  Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
              RFC 2671, DOI 10.17487/RFC2671, August 1999,
              <http://www.rfc-editor.org/info/rfc2671>.

   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, DOI 10.17487/RFC3490, March 2003,
              <http://www.rfc-editor.org/info/rfc3490>.

   [RFC3491]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)",
              RFC 3491, DOI 10.17487/RFC3491, March 2003,
              <http://www.rfc-editor.org/info/rfc3491>.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              DOI 10.17487/RFC3596, October 2003,
              <http://www.rfc-editor.org/info/rfc3596>.

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   [RFC3743]  Konishi, K., Huang, K., Qian, H., and Y. Ko, "Joint
              Engineering Team (JET) Guidelines for Internationalized
              Domain Names (IDN) Registration and Administration for
              Chinese, Japanese, and Korean", RFC 3743,
              DOI 10.17487/RFC3743, April 2004,
              <http://www.rfc-editor.org/info/rfc3743>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <http://www.rfc-editor.org/info/rfc4034>.

   [RFC4343]  Eastlake 3rd, D., "Domain Name System (DNS) Case
              Insensitivity Clarification", RFC 4343,
              DOI 10.17487/RFC4343, January 2006,
              <http://www.rfc-editor.org/info/rfc4343>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <http://www.rfc-editor.org/info/rfc5890>.

   [RFC5891]  Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Protocol", RFC 5891,
              DOI 10.17487/RFC5891, August 2010,
              <http://www.rfc-editor.org/info/rfc5891>.

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <http://www.rfc-editor.org/info/rfc6761>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <http://www.rfc-editor.org/info/rfc6891>.

   [RFC6895]  Eastlake 3rd, D., "Domain Name System (DNS) IANA
              Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
              April 2013, <http://www.rfc-editor.org/info/rfc6895>.

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   [RFC6912]  Sullivan, A., Thaler, D., Klensin, J., and O. Kolkman,
              "Principles for Unicode Code Point Inclusion in Labels in
              the DNS", RFC 6912, DOI 10.17487/RFC6912, April 2013,
              <http://www.rfc-editor.org/info/rfc6912>.

   [RFC7094]  McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
              "Architectural Considerations of IP Anycast", RFC 7094,
              DOI 10.17487/RFC7094, January 2014,
              <http://www.rfc-editor.org/info/rfc7094>.

   [RFC7719]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 7719, DOI 10.17487/RFC7719, December
              2015, <http://www.rfc-editor.org/info/rfc7719>.

   [RFC7816]  Bortzmeyer, S., "DNS Query Name Minimisation to Improve
              Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
              <http://www.rfc-editor.org/info/rfc7816>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <http://www.rfc-editor.org/info/rfc7858>.

   [RFC7872]  Gont, F., Linkova, J., Chown, T., and W. Liu,
              "Observations on the Dropping of Packets with IPv6
              Extension Headers in the Real World", RFC 7872,
              DOI 10.17487/RFC7872, June 2016,
              <http://www.rfc-editor.org/info/rfc7872>.

   [Sullivan-Class]
              Sullivan, A., "The DNS Is Not Classy: DNS Classes
              Considered Useless", July 2016,
              <https://datatracker.ietf.org/doc/draft-sullivan-dns-
              class-useless/>.

   [Unicode]  The Unicode Consortium, "The Unicode Standard, Version
              9.0.0,", ISBN 978-1-936213-13-9, 2016,
              <http://www.unicode.org/versions/Unicode9.0.0/>.

   [Unicode-UAX15]
              Davis, M. and K. Whistler, "Unicode Normalization Forms",
              February 2016, <http://unicode.org/reports/tr15/>.

   [Unicode-USA31]
              Davis, M., "Unicode Identifier and Pattern Syntax", May
              2016, <http://unicode.org/reports/tr31/>.

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Appendix A.  Change Log

   RFC Editor: Please remove this appendix before publication.

A.1.  Changes from version -00 (2017-06-02) to -01

   o  Many editorial corrections

   o  Addition of new (some replacing prior placeholder) sections,
      especially to the list of issues with the current DNS design and
      notably including Section 3.13.

A.2.  Changes from version -01 (2017-06-06) to -02

   o  Improved the discussion ins several sections, including a somewhat
      muddled description in Section 3.7

   o  Revised the Introduction to make the context for this document
      somewhat more clear.

   o  Added several more references even though still not nearly enough
      to make this document a comprehensive bibliography (which is not
      intended).

   o  Many editorial corrections and a few added references.

A.3.  Changes from version -02 (2017-06-19) to -03

   o  Added Section 3.15, discussing pressures less related to content,
      and smaller amounts of new material elsewhere.

   o  Added some additional references and acknowledgments.

   o  Extensive editorial corrections and revisions for clarity.

Author's Address

   John C Klensin
   1770 Massachusetts Ave, Ste 322
   Cambridge, MA  02140
   USA

   Phone: +1 617 245 1457
   Email: john-ietf@jck.com

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